mdfaw-bits Sub-function BITS: Saving of
the significant bits in the flag byte mdfaw_bits

MDFAW 12.260 Function Description

The duty of this function is to calculate the driver’s requested torque as a function of accelerator pedal position (wped_w) and cruise control output (mrfgr_w). Separate values are provided for cylinder charge and ignition influences (mifal_w, mifa_w).

The throttle pedal characteristic is defined by maps, where through pedal position and engine speed, a factor (relative torque) is stored to help scale indicated torque between the minimum and maximum. The relative driver’s requested torque can have values ​​greater than 100% (pedal crossover). For reverse gear, a separate map is available that can be used on vehicles with automatic transmission. To enhance driving
comfort, a change in the driver’s requested torque limit can take place under certain conditions (load changes, overrun fuel cut-off and reinstatement, transition from part load to idle and vice versa. See sub-function DMFABEG).

The idle condition (B_ll) is set when the relative driver’s requested torque drops below the threshold MRFALLU and is reset when the threshold MRFALLO is exceeded. The cruise control condition (B_fgr) is set when the cruise controller output is greater than the output of the pedal characteristic. The integral component of the idle control (dmllri_w) is included in the driver’s request.

The change limitation for the driver’s requested torque (sub-function DMFABEG) is used to improve ride comfort and overrun fuel cut-off and smooth resumption of positive and negative load changes. With that, a DT1-element filtered torque loss (dmverl_w) is added behind the change limitation around jumps in the clutch torque to damp the connection or disconnection of load.

Overrun fuel cut-off/reinstatement

Via a PT1-filter, down-regulation of the target torques starting from the actual torque at zero takes place by overrun fuel cut-off; smooth resumption by up-regulation of the target torques starting from mizwmn_w to mimin_w. The filter time constants for up-regulation and down-regulation can be chosen independently of each other. One more time constant is made available for hard resumption and leaving idle (under light throttle). The initialization of the filters on the overrun fuel cut-off to the actual torque is needed to avoid a jump in torque on enabling of the ignition angle interventions. The filtering is, or is not cancelled:

- During active dashpot,

- For active load shock absorption,

- In the test laboratory

- On a steep negative speed gradient (uncoupling of thrust or throttle),

- When the clutch is actuated (configurable via CWDMFAB)

- mrfa gradient at higher threshold (important during hard resumption and when leaving the idle),

- Upon reaching the basic ignition angles.

Dashpot

The change limitation for negative load changes (dashpot) is implemented using a
PT1-filter with gear and speed-dependent time constant. The PT1-filter runs at
a negative gradient of the unfiltered driver’s requested torque. The dashpot is
triggered when the difference between the filtered and unfiltered output value
exceeds a clutch-dependent and torque-dependent threshold, and cruise control
is not engaged. The trigger also always occurs at the transition to idle. The
PT1-filter triggered by the dashpot is initialized with the actual torque in
order to avoid a jump in torque during ignition angle interventions. The
dashpot is terminated when the difference between filtered and unfiltered value
falls below a gear-dependent threshold. As long as the dashpot is active, there
will not be any overrun fuel cut-off (see function %BBSAWE).

The driver’s desired torque for the cylinder charge influence mifal_w is calculated by a dashpot with its own PT1-filter that is initialized when the unfiltered driver’s desired torque drops below the trigger level. In this way, a steep initial drop is reached, which leads to the rapid closing of the throttle. Then a soft change is made to the target value. The dashpot can be active only when:

- The general dashpot-enable is done viaCWDMFAB Bit1,

- There is no commitment to overrun fuel cut-off,

- Load shock absorption is not active,

- There is the speed signal,

- The minimum speed is exceeded for dashpot,

- The clutch is not pressed,

- Start end is reached,

- The response is greater than zero,

- ASR intervention is not active,

- The cylinder charge is greater than the minimum charge.

Load Shock Absorption

The change limitation during positive load changes is realized with the help of a PT2 filter whose damping and time constant are gear- and speed-dependent. The PT2 filter runs with a positive gradient of the unfiltered driver’s requested torque. Load shock damping is triggered when the difference between unfiltered and filtered output value exceeds a gear- and clutch torque-dependent threshold. The PT2 filter is triggered when the load shock absorption is initialized with the actual torque or a speed-and gear-dependent initial value, to avoid a jump in torque upon enabling of the ignition angle interventions and to influence the response behavior. The load shock damping is terminated when the difference between the filtered and unfiltered value drops below a gear-dependent threshold.

The driver’s desired torque for the cylinder charge influence mifal_w with active load shock damping is calculated from a map which depends on the desired torque for the ignition influence (mifa_w) and on the gear, which is a limitation on the unfiltered target. Thus, the cylinder charge can be controlled so that there is no significant ignition angle intervention in order to set the desired torque curve.

The load shock damping can be active only when

- Load shock damping is generally enabled via CWDMFAB Bit 0,

- There is no idle

- For vehicles with CVT transmission, the torque gradient limitation is not active and the torque converter clutch is not open,

- The speed signal is present

- The minimum speed for load shock absorption is exceeded,

- The clutch is not actuated

- Cruise control is not engaged,

- Speed ​​and speed limits are not active,

- End of start conditions is reached,

- The gear is greater than zero,

- No traction control intervention is active.

The PT2 filter is implemented with two integrators and feedback. There is also the possibility that the filter is initialized with a given value (iwflsd_w) if the condition B_iflsd is set.